The present invention achieves advantages as a circuit to compensate for RMR variations and to compensate for shunt resistance across RMR in an open loop current bias architecture. Prior designs use open loop Ibias architecture which has around a 3% variation in bias current over typical RMR ranges and that does not compensate for shunt resistance across the RMR. In addition, newer designs target TGMR heads which are around four times higher resistance than prior design specifications with the resulting error in open loop designs being greater than 10%. Further, the shunt resistance is inherent if a high band-width resistive feedback amplifier is used as a sensing amplifier. The feedback resistors appear in parallel to the RMR (resistive sensor) shunting away bias current intended for the RMR. The present invention uses a gm amplifier that senses the voltage across the RMR and adjusts the bias to compensate for its resistance and for shunt resistance. The method does so without measuring the value of the RMR directly.